2245 etc bias transistor upgrade

[Mike Sweeney]

Here is the final outcome of my own version of the round to TO transformation.

All I did was reverse the bend for the diode, get a longer screw and put the new transistor on some lead extensions. And yes, there is a mica insulator between the heatsink and the body of the transistor with a dab of thermal compound. I could put a small tie wrap on the curl but I think that is overkill.

 

[jd3rdcoast]

What part number did you use for the trimmer resistors? Nice work!

 

[Jonstigator]

Looks nice.

yes trimming resistor. 5k OHM ? 300 OHM?

 

[Mike Sweeney]

What part number did you use for the trimmer resistors? Nice work!

They were hard to find in stock - Both pots were 2.2K despite what the parts list said in the service manual. I found a guy on the auction site with a pile of them. If they are knock offs, they are the best I've ever seen. I think they are the real deal. I bought 10 and then after I got them and used them, I went back and bought 20 more . Just in case..

3386H-1-222LF Bourns, 2.2K ohm 0.50W

 

[Jonstigator]

Both pots were 2.2K despite what the parts list said in the service manual.

I took the trimmers off one channel of my 2220b. One measured 304 Ohms and the other 4.4 KOhms (out of tolerance.) I am thinking the manual is correct in my case. What is not listed is the wattage rating. Do you think I would be fine with going 1/2 watt?

 

[Mike Sweeney]

1/2 watt is plenty for a trimmer. The only fun aspect is getting the right orientation of the trimmer and if you want a multi turn or single turn. Sometimes with certain values you don't have a choice. My 2.2K with the side mount are single turn only which makes adjustments a bit temperamental